L9214A/G
Low-Cost Ringing SLIC
Preliminary Data Sheet
October 2001
Typically IBIAS is 3.5 mA. This additional VBAT1 current
contributes to the loop current and the remaining loop
current is supplied by VBAT2, so that
Applications
Power Control
IVBAT2 = IQ2 + ILOOP – IBIAS
Under normal device operating conditions, power dissi-
pation must be controlled to prevent the device temper-
ature from rising too close to the thermal shutdown
point. Power dissipation is highest with higher battery
voltages, higher current limit, and under shorter dc loop
conditions. Additionally, higher ambient temperature
will reduce thermal margin. Increasing the number of
PC board layers and increasing airflow around the
device are typical ways of improving thermal margin.
IVCC is the current drawn from VCC and is relatively con-
stant as the phone goes off hook.
The total power from the power supplies is:
PTOTAL = {[(IQ1 + IBIAS) * VBAT1] + [(IQ2 + ILOOP – IBIAS) *
VBAT2] + [(IVCC) * VCC]}
The maximum values of IQ1 and IQ2 are 1.95 mA and
1.20 mA respectively from Table 4.
The maximum recommended junction temperature for
the L9214 is 150 °C. The junction temperature is:
If the current limit is set to 25 mA, given the current limit
tolerance of 10%, the maximum current limit is
27.5 mA. Also, assume 20 Ω of wire resistance, 30 Ω
of protection resistance, and 200 Ω for the handset
Tj = TAMBIENT + θJA * PSLIC
The thermal impedance of this device depends on the
package type as well as number of PCB layers and air-
flow. The thermal impedance of the 28-pin SOG pack-
age is somewhat higher than the 32-pin PLCC
package. The 28-pin SOG package in still air with a
single-sided PCB is rated at 70 °C/W. The 32-pin
PLCC package thermal impedance with no airflow on a
four-layer PCB is estimated at 37 °C/W.
PTOTAL = {[(1.95 mA + 3.5 mA) * (65 V)] + [(1.20 mA +
27.5 mA – 3.5 mA) * (21 V)] + [(6 mA) * (5 V)]
= 913.45 mW
The power delivered to the loop and the protection
resistors (PLOOP) is:
PLOOP = {(ILOOP)2 * [(2 * RPROTECTION) + (RWIRE) +
(RPHONE)]} = {(27.5 mA)2 * [(2 * 30 Ω) + (20 Ω) +
200 Ω)]} = 212 mW
The power handling capability of the package is:
PSLIC = (150 °C – TAMBIENT)/θJA
Thus, the total power dissipated by the SLIC is:
which is a minimum of 0.93 W for the 28-pin SOG
package with a single-sided PCB and no airflow and as
much as 2.15 W for the 32-pin PLCC package with a
multilayer PCB.
PD of SLIC = Total power (PTOTAL) – power delivered to
loop and protection resistors (PLOOP).
PD = 913.45 mW – 212 mW
= 701.45 mW for this example.
This device is intended to operate with a high-voltage
primary battery of –63 V to –70 V. Under short-loop
conditions, an internal soft battery switch shunts most
(all but IBIAS = 3.5 mA) of the loop current to an auxiliary
battery of lower absolute voltage (typically –21 V).
Where single battery operation is required, an external
power control resistor can be connected from the VBAT2
pin to VBAT1 and all but 3.5 mA of the loop current will
flow through the power control resistor.
Since the minimum power handling capability of the
28-pin SOG package is 0.93 W, in this case either
package type is acceptable even with a single-sided
PCB. At higher battery voltages, higher ambient tem-
perature, and higher current limit, the required thermal
impedance drops and the 32-pin PLCC package, more
PCB layers, or some airflow might be required.
Another case to consider is the case of the power con-
trol resistor. In this case, the effective VBAT2 voltage is:
The power dissipated in the device is best illustrated by
an example. Assume VBAT1 is –65 V, VBAT2 is –21 V,
and the current limit is is ILOOP.
VBAT2 = VBAT1 – RPWR * (ILOOP – IBIAS + IQ2)
For the case of the 27.5 mA maximum current limit,
choosing RPWR = 1.75 kΩ would give VBAT2 = –21 V and
the same SLIC power as above. The power in the
resistor would be:
Let IQ1 and IQ2 be the quiescent currents drawn from
VBAT1 and VBAT2 respectively (the current drawn from
the battery when the phone is on-hook). Let IBIAS be
the additional current drawn from VBAT1 when the
phone is off-hook.
PRPWR = (ILOOP – IBIAS + IQ2)2 * RPWR = 1.11 W
Choosing a larger RPWR would result in lower VBAT2 and
lower SLIC power, but more power in the resistor. Simi-
larly, choosing a smaller RPWR results in higher VBAT2,
higher SLIC power, and less power in the resistor.
IBIAS = IVBAT1(off-hook) – IQ1
24
Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
